The U.S. Environmental Protection Agency has determined that thousands of Audi, Porsche and Volkswagen models equipped with a 3.0-liter V6 diesel engine also contain a defeat device.

The U.S. Environmental Protection Agency has determined that thousands of Audi, Porsche and Volkswagen models equipped with a 3.0-liter V6 diesel engine also contain a defeat device.

In the second notice of violation of the Clean Air Act, the EPA informed the automakers that they "developed and installed" defeat devices on a number of models including the 2014 Volkswagen Touareg, the 2015 Porsche Cayenne and the 2016 Audi A6, A7, A8 / A8 L and Q5.

As the EPA explains, Volkswagen "manufactured and installed software in the electronic control module of these vehicles that senses when the vehicle is being tested for compliance with EPA emissions standards. When the vehicle senses that it is undergoing a federal emissions test procedure, it operates in a low NOx 'temperature conditioning' mode. Under that mode, the vehicle meets emission standards. At exactly one second after the completion of the initial phases of the standard test procedure, the vehicle immediately changes a number of operating parameters that increase NOx emissions and indicates in the software that it is transitioning to 'normal mode' where emissions of NOx increase up to nine times the EPA standard."

The EPA says 10,000 models have been sold in the United States since 2014 but the notice of violation also covers an undisclosed number of 2016 models.

In a statement, the EPA's Cynthia Giles said “VW has once again failed its obligation to comply with the law that protects clean air for all Americans." She went on to say “All companies should be playing by the same rules. EPA, with our state, and federal partners, will continue to investigate these serious matters, to secure the benefits of the Clean Air Act, ensure a level playing field for responsible businesses, and to ensure consumers get the environmental performance they expect.”

Her sentiments were echoed by the California Air Resources Board Executive Officer Richard Corey who stated "These tests have raised serious concerns about the presence of defeat devices on additional VW, Audi and Porsche vehicles. Today we are requiring VW Group to address these issues."